Hello Matt,
I guess that is a BUG in the SM 15.x latest version. I'm using the SM 15.x for the MX Inbound Gateway only and in the dashboard have the information Top Outbound IP Addresses with values and Top Inbound IP Address with blank. But, I only have a inbound connections to this server.
If possible I'd like more information about this Dashboard because using only has Gateway the Top Inbound Sender, Top Inbound IP and Top Inbound Domains are blank.
Regards, Cleber